In conventional medical diagnostic imaging, the object is to obtain an image of a patient's internal anatomy with as little X-radiation exposure as possible. The fastest imaging speeds are realized by mounting a duplitized radiographic element between a pair of fluorescent intensifying screens for imagewise exposure. About 5% or less of the exposing X-radiation passing through the patient is adsorbed directly by the latent image forming silver halide emulsion layers within the duplitized radiographic element. Most of the X-radiation that participates in image formation is absorbed by phosphor particles within the fluorescent screens. This stimulates light emission that is more readily absorbed by the silver halide emulsion layers of the radiographic element.
Examples of radiographic element constructions for medical diagnostic purposes are provided by U.S. Pat. No. 4,425,425 (Abbott et al.), U.S. Pat. No. 4,425,426 (Abbott et al.), U.S. Pat. No. 4,414,310 (Dickerson), U.S. Pat. No. 4,803,150 (Dickerson et al.), U.S. Pat. No. 4,900,652 (Dickerson et al.), U.S. Pat. No. 5,252,442 (Tsaur et al.), and U.S. Pat. No. 5,576,156 (Dickerson), and Research Disclosure, Vol. 184, August 1979, Item 18431.
Problem to be Solved
The earliest radiographic elements typically comprised a silver halide emulsion coated on a single side of a glass substrate. More recently, radiographic elements or materials described and used in the art have traditionally contained various silver halide emulsion layers coated on a transparent film support (often coated on both sides) so the resulting images can be viewed using light boxes. However, in many remote parts of the world, light boxes are not available, thereby severely limiting the usefulness of traditional radiographic elements.
Chest radiography is one of the most common uses of radiographic imaging in the world. However, because of the nature of the organs in the chest cavity, imaging has been limited to using high-powered, fixed installation X-radiation generating equipment. Based on an American College of Radiology (“ACR”) clinical practice standard, chest radiography should be performed at exposure times less than 40 milliseconds (less than 15 milliseconds for pediatric patients). This is necessary in order to stop the motion of the beating heart and adjacent blood vessels as well as to stop the motion of the surrounding lung tissues (respiration-induced motion and cardiac motion). While most patients can hold their breath for a brief time, the most critically ill patients cannot do so, further exacerbating this problem.
Additionally, a 10:1, 103 line/mm anti-scatter grid is recommended by the ACR in order to reduce scattered radiation, putting additional stress on the X-radiation exposure system. An unusually long X-radiation tube focus-film distance of 72 inches (178 cm) (40 inches or 102 cm for portable exams) is recommended in order to minimize X-radiation tube focal spot image blur. This long focus-film distance reduces the intensity of the X-radiation beam to about 25% of its normal intensity, further limiting the utility of low-powered X-radiation units. A radiographic system speed of 200 is recommended, based on existing commonly available screen/film/processing technology.
Given these standardized exposure conditions and radiographic technique considerations, inexpensive (low-powered) x-ray generators cannot produce clinically acceptable, motion-artifact-free chest radiographs using available screen-radiographic film systems that have unacceptably low system speed.
For imaging systems with substantially reduced image blur and high speed, experience has taught us that high system speed and high clinical image quality are not mutually exclusive.
In addition, for imaging systems with the primary advantage of very high speed, reducing or eliminating concerns about patient motion during radiographic exposures with low-powered X-radiation equipment will make clinically useful chest radiography a practical examination for the first time with such equipment. Currently, the only solution to this problem is to use full-powered X-radiation generators that are not affordable in most of the developing countries of the world.
In addition, in many parts of the world, there is insufficient electrical power to generate X-radiation using traditional imaging machines and such high power X-radiation generators are usually located in “fixed” installation and not portable into remote regions.
Thus, high-powered X-radiation generating equipment is not generally available in situations such as mobile military radiography, field veterinary medicine, on-site sports radiography, and some industrial/security radiography where portability and low electrical power requirements are essential. In these and other applications, very high speed screen-film materials are critical to the ability of the radiographic systems to make a properly exposed radiograph and stop patient motion by using short exposure times with limited X-radiation tube output.
Thus, there is a need to find a means to provide meaningful radiographic imaging and diagnostics without the need for a light box so the image can be viewed under ambient lighting. In addition, it would be useful to find a way to accurately and effectively image patients with minimal X-radiation exposure using low power X-radiation generators for radiographic uses including chest radiography.